Obsessive compulsive disorder (OCD) is chronic, debilitating and prevalent. Adult OCD has recently received much research attention. Medications with potent serotonin reuptake blocking effects are of substantial help to approximately 50% of such patients. The investigational drug chlorimipramine (CMI) is the most widely studied, but fluoxetine appears equally promising in open clinical trials. If effective in controlled studies, fluoxetine has important advantages over CMI, such as already being marketed in the U.S. for depression, and what appear to be more favorable safety and side effect profiles. OCD is common in childhood and adolescence, with recent estimates of 200,000 or more such cases in the U.S.. Despite evidence that is a paucity of research in childhood/adolescent OCD. The few studies that do exist suggest phenomenological and pharmacological similarities to the adult form, and CMI appears effective. There are, however, no reported studies of fluoxetine in this age group. Despite this, practitioners are now using fluoxetine for childhood and adolescent OCD because of the drug's availability. Based on promising pilot data, an 8 week placebo controlled evaluation of fluoxetine in adolescent OCD is proposed. Seventy five patients will be randomized to drug or placebo. Patients responding by the end of 8 weeks to either treatment will be continued on a double blind basis for an 8 week maintenance phase to test the durability of response and whether further improvement occurs. The immediate goal is to assess whether fluoxetine is effective for the acute treatment of adolescent OCD. Long term goals are to establish guidelines for both the acute and long term pharmacological and psychosocial treatment of childhood/adolescent OCD, and to understand its pathophysiology. Intervention at a young age may be more effective that in the often more chronic adults form, and also prevent long term suffering and impairment.